Check whether the calculator asks for your income, regular spending, deposit, mortgage term and any existing debts, as these can affect the estimate. Find out which interest rate it uses and whether the result includes arrangement fees, valuation costs or other charges. Treat the figure as a guide rather than a mortgage offer, because lenders apply their own affordability and credit checks. For a more tailored view, compare results from FCA-authorised lenders or speak to a regulated mortgage adviser.